Record the readahead pattern in ra->pattern and extend ra_submit()
parameters, to be used by the next readahead tracing/stats patches.
7 patterns are defined:
pattern readahead for
-----------------------------------------------------------
RA_PATTERN_INITIAL start-of-file read
RA_PATTERN_SUBSEQUENT trivial sequential read
RA_PATTERN_CONTEXT interleaved sequential read
RA_PATTERN_OVERSIZE oversize read
RA_PATTERN_MMAP_AROUND mmap fault
RA_PATTERN_FADVISE posix_fadvise()
RA_PATTERN_RANDOM random read
Note that random reads will be recorded in file_ra_state now.
This won't deteriorate cache bouncing because the ra->prev_pos update
in do_generic_file_read() already pollutes the data cache, and
filemap_fault() will stop calling into us after MMAP_LOTSAMISS.
CC: Ingo Molnar <mingo@xxxxxxx>
CC: Jens Axboe <axboe@xxxxxxxxx>
CC: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Acked-by: Jan Kara <jack@xxxxxxx>
Acked-by: Rik van Riel <riel@xxxxxxxxxx>
Signed-off-by: Wu Fengguang <fengguang.wu@xxxxxxxxx>
---
include/linux/fs.h | 36 +++++++++++++++++++++++++++++++++++-
include/linux/mm.h | 4 +++-
mm/filemap.c | 3 ++-
mm/readahead.c | 29 ++++++++++++++++++++++-------
4 files changed, 62 insertions(+), 10 deletions(-)
--- linux-next.orig/include/linux/fs.h 2012-01-25 15:57:47.000000000 +0800
+++ linux-next/include/linux/fs.h 2012-01-25 15:57:50.000000000 +0800
@@ -952,11 +952,45 @@ struct file_ra_state {
there are only # of pages ahead */
unsigned int ra_pages; /* Maximum readahead window */
- unsigned int mmap_miss; /* Cache miss stat for mmap accesses */
+ u16 mmap_miss; /* Cache miss stat for mmap accesses */
+ u8 pattern; /* one of RA_PATTERN_* */
+
loff_t prev_pos; /* Cache last read() position */
};
/*
+ * Which policy makes decision to do the current read-ahead IO?
+ *
+ * RA_PATTERN_INITIAL readahead window is initially opened,
+ * normally when reading from start of file
+ * RA_PATTERN_SUBSEQUENT readahead window is pushed forward
+ * RA_PATTERN_CONTEXT no readahead window available, querying the
+ * page cache to decide readahead start/size.
+ * This typically happens on interleaved reads (eg.
+ * reading pages 0, 1000, 1, 1001, 2, 1002, ...)
+ * where one file_ra_state struct is not enough
+ * for recording 2+ interleaved sequential read
+ * streams.
+ * RA_PATTERN_MMAP_AROUND read-around on mmap page faults
+ * (w/o any sequential/random hints)
+ * RA_PATTERN_FADVISE triggered by POSIX_FADV_WILLNEED or FMODE_RANDOM
+ * RA_PATTERN_OVERSIZE a random read larger than max readahead size,
+ * do max readahead to break down the read size
+ * RA_PATTERN_RANDOM a small random read
+ */
+enum readahead_pattern {
+ RA_PATTERN_INITIAL,
+ RA_PATTERN_SUBSEQUENT,
+ RA_PATTERN_CONTEXT,
+ RA_PATTERN_MMAP_AROUND,
+ RA_PATTERN_FADVISE,
+ RA_PATTERN_OVERSIZE,
+ RA_PATTERN_RANDOM,
+ RA_PATTERN_ALL, /* for summary stats */
+ RA_PATTERN_MAX
+};
+
+/*
* Check if @index falls in the readahead windows.
*/
static inline int ra_has_index(struct file_ra_state *ra, pgoff_t index)
--- linux-next.orig/mm/readahead.c 2012-01-25 15:57:49.000000000 +0800
+++ linux-next/mm/readahead.c 2012-01-25 15:57:50.000000000 +0800
@@ -249,7 +249,10 @@ unsigned long max_sane_readahead(unsigne
* Submit IO for the read-ahead request in file_ra_state.
*/
unsigned long ra_submit(struct file_ra_state *ra,
- struct address_space *mapping, struct file *filp)
+ struct address_space *mapping,
+ struct file *filp,
+ pgoff_t offset,
+ unsigned long req_size)
{
int actual;
@@ -382,6 +385,7 @@ static int try_context_readahead(struct
if (size >= offset)
size *= 2;
+ ra->pattern = RA_PATTERN_CONTEXT;
ra->start = offset;
ra->size = min(size + req_size, max);
ra->async_size = 1;
@@ -403,8 +407,10 @@ ondemand_readahead(struct address_space
/*
* start of file
*/
- if (!offset)
+ if (!offset) {
+ ra->pattern = RA_PATTERN_INITIAL;
goto initial_readahead;
+ }
/*
* It's the expected callback offset, assume sequential access.
@@ -412,6 +418,7 @@ ondemand_readahead(struct address_space
*/
if ((offset == (ra->start + ra->size - ra->async_size) ||
offset == (ra->start + ra->size))) {
+ ra->pattern = RA_PATTERN_SUBSEQUENT;
ra->start += ra->size;
ra->size = get_next_ra_size(ra, max);
ra->async_size = ra->size;
@@ -434,6 +441,7 @@ ondemand_readahead(struct address_space
if (!start || start - offset > max)
return 0;
+ ra->pattern = RA_PATTERN_CONTEXT;
ra->start = start;
ra->size = start - offset; /* old async_size */
ra->size += req_size;
@@ -445,14 +453,18 @@ ondemand_readahead(struct address_space
/*
* oversize read
*/
- if (req_size > max)
+ if (req_size > max) {
+ ra->pattern = RA_PATTERN_OVERSIZE;
goto initial_readahead;
+ }
/*
* sequential cache miss
*/
- if (offset - (ra->prev_pos >> PAGE_CACHE_SHIFT) <= 1UL)
+ if (offset - (ra->prev_pos >> PAGE_CACHE_SHIFT) <= 1UL) {
+ ra->pattern = RA_PATTERN_INITIAL;
goto initial_readahead;
+ }
/*
* Query the page cache and look for the traces(cached history pages)
@@ -463,9 +475,12 @@ ondemand_readahead(struct address_space
/*
* standalone, small random read
- * Read as is, and do not pollute the readahead state.
*/
- return __do_page_cache_readahead(mapping, filp, offset, req_size, 0);
+ ra->pattern = RA_PATTERN_RANDOM;
+ ra->start = offset;
+ ra->size = req_size;
+ ra->async_size = 0;
+ goto readit;
initial_readahead:
ra->start = offset;
@@ -483,7 +498,7 @@ readit:
ra->size += ra->async_size;
}
- return ra_submit(ra, mapping, filp);
+ return ra_submit(ra, mapping, filp, offset, req_size);
}
/**
--- linux-next.orig/include/linux/mm.h 2012-01-25 15:57:47.000000000 +0800
+++ linux-next/include/linux/mm.h 2012-01-25 15:57:50.000000000 +0800
@@ -1448,7 +1448,9 @@ void page_cache_async_readahead(struct a
unsigned long max_sane_readahead(unsigned long nr);
unsigned long ra_submit(struct file_ra_state *ra,
struct address_space *mapping,
- struct file *filp);
+ struct file *filp,
+ pgoff_t offset,
+ unsigned long req_size);
/* Generic expand stack which grows the stack according to GROWS{UP,DOWN} */
extern int expand_stack(struct vm_area_struct *vma, unsigned long address);
--- linux-next.orig/mm/filemap.c 2012-01-25 15:57:47.000000000 +0800
+++ linux-next/mm/filemap.c 2012-01-25 15:57:50.000000000 +0800
@@ -1597,11 +1597,12 @@ static void do_sync_mmap_readahead(struc
/*
* mmap read-around
*/
+ ra->pattern = RA_PATTERN_MMAP_AROUND;
ra_pages = max_sane_readahead(ra->ra_pages);
ra->start = max_t(long, 0, offset - ra_pages / 2);
ra->size = ra_pages;
ra->async_size = ra_pages / 4;
- ra_submit(ra, mapping, file);
+ ra_submit(ra, mapping, file, offset, 1);
}
/*
--
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